Microwave frequency cavity resonator structure



S. F. VARIAN July 7, 1953 MICROWAVE FREQUENCY CAVITY nssonxroamuc'ruan Filed Marh 26, 1949 3 Sheets-Sheet 1 INVENTOR 15' www E VWP/fl/V Y fi/KM ATTORNEY MICROWAVE FREQUENCY CAVITY RESONATOR Filed March 26, 1949 July 7, 1953 3 Sheets-She t 2 gwfily INVENTOR 5/611/20 E VQ/P/fl/V fi A ,44 a? ATTORNEY Patented July 7, 1953 MICROWAVE FRE UENCY-CAVITY RESONATOR STRUCTURE Sigurd F. Varian,.S.tanford, (la-lift, assignor to The Sperry C0rp0ration', Great Neck, N. Y., a corporation of Delaware Application March 26, 1949; Serial No. 83,730

16 Claims.

This invention relates to improved microwave frequency cavity resonator apparatus.

In prior art electron discharge tubes using one or more cavity resonators, the resonators. are invariably designed, from the structural or physical standpoint, as symmetricalfigures of revolution about the axis of the beam of electrons. The multiresonator prior art discharge tube usually has a plurality of radially symmetrical, cascaded resonators aligned along the tubes electron beam axis. In structure, the cascaded resonators resemble short sections of coaxial line closed at both ends with a capacity loading section at one end thereof.

For tuning the prior artdischarge tubes, use is made of paddle, plunger or gridtuners. In the grid tuning scheme, the parallel spacing between the grids is changed. For the purpose of changing the grid gap, the grids are connected to the flexible walls of the cavities by motion translating structure; considerable structure consisting of resiliently biased shanks, springs and control screws are necessarily mounted upon and made integral with the tube structure to activate the flexible Walls and thus change the grid gap distance. It is difiicult in using suchgrid tuners to maintain the grids in parallel relationship. Paddle and plunger tuners involve, respectively, paddles connected to resiliently biased 'rotational shanks or rods, and translatable plungers. These tuners project into the cavity chambers from mountings on the peripheries of the cavities. The paddle and plunger tuners operate upon the principle of moving conducting bodies in the cavities to disturb the electromagnetic fields therein. The cavity Q is lowered by these tuners because of the presence of foreign conducting bodies in the cavity resonators. Furthermore, the hermetical seals associated with such tuning structures have proven to be sources of trouble.

All told, the prior art discharge tubes incorporating one or more cavity resonators consist of complex structures that. are time consuming.

to manufacture from the machinists, assemblers and designers standpoints. Consequently, such devices are relatively expensive to build.

It has become clear, therefore, that there is a need for a microwave frequency cavity resonator having a simplified geometry that is accordingly more economical to manufacture than the corresponding complex and expensive prior art devices. A cavity resonator defined by'a drumshaped interior having a capacitance loading I.* II)- section comprising at least one conducting 'arm projecting into: the interior thereof successfullysatisfies the aforesaid desired needs. The conducting arm extends from a tubular inner 'surface region of the resonator chamber toward the In contrast with the" opposite region thereof. prior' .art discharge tubes, from a structural standpoint, the microwave frequency tube of the present invention have the axis of the beam of electrons extending along a path intersecting the tubular inner walls of the cavity resonator; in other words, the axis of symmetry of the cavity is perpendicular to the axis of the beam of electrons, Moreover, in a multi-resonator dis-v Charge" tube, the cavities are uniquely arranged in diametral alignment along the axis of the beam of electrons, and one or each of the end Walls of. the drum-shaped cavities may consist of a diaphragm that serves as a tuner for the cavities. I v

Pursuant tothe presentinvention, it will" be seen that tnedischarge tube using one or more cavity resonators maynow be mademerely from anasscmbledstructure consisting of a prefabricated block of conducting material, and prefabricated tubular conducting bodies and face stampings. "For a multi-resonator discharge. tube in particular, the main body of the discharge tube consists of a drilled'or bored block of conducting material, for example, oxygen free copper. In'the fabrication of the resonatorstructure, the solid block of conducting material is simply placed in a drill-jig or bore-jig and drilled or bored transversely and vertically 'to provide a proper number of bores or passages ofap-propriate sizes. Certain of the transverse bores are in diametra-l alignment to define the cylindrical inner surfaces of the cavitychambers; other transverse bores are made to receive the coupling members. The vertical bore or passage is made for the purpose of mounting'the reentrant posts. ,At the conclusion ofthis relativelyeconomical and simple operation, the drilled block is availablefor assembly. Drift tube inserts carrying electron-permeable grids atthe ends thereof are inserted into the ver-'- tical bore and clamped into position. Prefabricated diaphragm stampings, or facestampings carrying diaphragms, are mounted at the op-" posite open ends of the cavitybores to define the drum-shaped cavity. resonators. Differential screw mechanisms may be mounted upon the face stampings" for the purpose of activating the di a d Co p i g members'are readily inserted intothe transverse bores therefor'to' 3 couple the cavities to external apparatus. At this point, the assembled cavity structure is readily available for mounting upon a cathode structure.

It will be seen, furthermore, that an assembled resonator structure may also be made merely from prefabricated metallic tubes and prefabricated face stampings pursuant to the present invention. For a discharge tube using three resonator cavities, three prefabricated diametrally aligned tubular bodies are enclosed by prefabricated face stampings. These bodies have cylindrical inner surfaces defining the inner surfaces of the cavity resonators, and they carry aligned tubular reentrant posts.

The two face stampings positioned at the opposite open ends of the diametral aligned tubes form end walls and cooperate with the tubular inner surfaces to define drum-shaped cavity resonators. Diaphragms are mounted at diametrally aligned openings in one of the end walls to tune the cavities to frequencies of operation, and coupling connectors are mounted at aligned openings in the other end wall to couple the cavities to external apparatus. The cathode structure is mounted at a further face stamping to permit the electron stream to flow along a path intersecting the tubular inner surfaces of the cavities. A hollow interior is defined between the outer surfaces of the tubular bodies and the inner surfaces of the face stampings in which a cooling fluid may be circulated for the purpose of cooling the cavities during the operation of the discharge tube.

Consequently, cavity resonator structure for one or more cavities fashioned from, according to one version, a drilled or bored block of conducting material, and prefabricated tubular conducting bodies and face stampings, or according to another version, merely from prefabricated tubular conducting bodies and face stampings in accordance with the present invention afford a relatively simple and economical discharge tube that can be manufactured in mass production. Furthermore, these advantages are obtained without sacrificing the electrical advantages present in the prior are discharge tubes.

The drum-shaped cavity permits a scheme of volume tuning that avoids the inherent difficulties associated With the paddle, plunger, and grid tuners of the prior art discharge devices. For volume tuning the drum-shaped cavities, diaphragms are mounted at the open ends of the drum-shaped cavities, and differential screw mechanisms may be mounted on the face stampings to activate the diaphragms. Furthermore, the diaphragm volume tuner possesses substantial electrical and mechanical advantages over the paddle, plunger, and grid tuners. For example, it is possible with the volume tuner to tune the cavities with two independent tuners, that is, one diaphragm at each end of the drumshaped cavities. Consequently, independent, coarse and vernier tuning of each cavity is obtainable. Moreover, factory pretuning of each cavity is also made possible. The flexibility of volume tuning is further emphasized by the fact that a gang tuning arrangement may be easily arranged on one face stamping of a multi-resonator discharge tube.

The volume tuner in contrast to paddle and plunger tuners, avoids the mechanical difliculties associated with hermetical seals, and furthermore the differential screw mechanism activating the diaphragm of the volume tuner is not encumbered by a short operating life common to the mechanisms of paddle tuners. In contrast to paddle and plunger tuners, the diaphragm volume tuning has a negligible effect upon the cavity Q, because no added current path is introduced into the cavity chambers. It will also be understood that secondary loading effects, a possibility whenever a paddle or plunger tuners are used, are also avoided by the diaphragm volume tuner.

With respect to the grid tuner, the diaphragm volume tuner avoids the inherent difficulty of maintaining the parallel grid relationship associated with grid tuners. Furthermore, tube structure incorporating the diaphragm volume tuner is relatively less sensitive to atmospheric pressure as compared to the conventional discharge tube employing grid tuning, because the latter embodies a relatively larger flexible wall surface; in contrast, the diaphragm of a corresponding volume tuner is relatively smaller in surface area. This advantage is especially appreciated when the discharge tube is used in airborne equipment.

It is, therefore, the principal object of this invention to provide a cavity resonator geometry such that assembled, prefabricated bodies of conducting material defining such a resonator, or a plurality thereof, require a minimum of design, machine and assembly work in the fabrication thereof and also in the incorporation thereof into microwave tube structure.

It is, therefore, an important object of this invention to provide a cavity resonator geometry such that assembled prefabricated bodies of end walls, reentrant posts and a block of conducting material, or assembled prefabricated units of face stampings and tubular bodies, defining such a resonator, or a plurality thereof, require the minimum of design, machine, and assembled work in the fabrication thereof and also in the incorporation thereof into microwave tube structure.

A further object of this invention is to provide for microwave tube structure incorporating a drum-shaped cavity resonator, or a plurality thereof in diametral alignment, in which the linear electron stream path intersects the tubular inner surface of the single resonator, or the tubular inner surfaces of the cavities of the multi-resonator unit.

Another object of this invention is to provide a drum-shaped cavity resonator, or an arrangement of a plurality of such cavities, that induces a low-loss volume tuning scheme which may include independent, coarse and vernier trim tuning by predetermined amounts of each resonator, and which may also include a gang tuning arrangement for the plurality of resonators.

A further object of this invention is to provide a cavity resonator, or an arrangement of a plurality of such resonators, that can be made from a solid block of conducting material by simply drilling, boring, or the like, the block of conducting material.

A further object of this invention is to provide for microwave tube structure incorporating a cavity resonator, or a plurality thereof, from tubular conducting bodies and conductive face stampings in which there is defined a hollow interior between the inner surfaces of the face stampings and the outer surfaces of the tubular bodies; a cooling fluid may be provided to circulate in the interior to cool the apparatus during operation.

The invention also relates to the novel features or principles of the instrumental-ities described herein, whether or not such are used for the stated objects, or in the stated fields or combinations.

These and other objects and advantages of the invention will become apparent in the following specification and drawings of which:

Fig. 1 is a perspective view of components constituting an approved embodiment of a cavity Fig. 5 is a longitudinal view, partly in section,

of the embodiment of Fig. 2; I

Fig. '6 is a longitudinal view, partly in section, of a modified embodiment;

Fig. '7 is a view taken along line I| of Fig. 6; Fig. 8 is a longitudinal view, partly in section, of another modification of the embodiment and Fig. 9 is a view, partly in section, taken along line 99 of Fig. 8.

A description of discharge tube apparatus constructed in accordance with the present invention follows: Figs. 1-5 show a multi-resonator device including a body I formed of a block of conducting material having three bores I, '8 and 9. The bores I, 8 and 9 are diametrically aligned, and they form the tubular inner surfaces of the three drum-shaped cavity'resonators.

With a given D. C. input power, there are definite upper limits to the gain of a two-resonator amplifier discharge tube. However, correspondingly higher gain is obtainable when more than one stage of' amplification is used. Instead of coupling the output of a simple two-resonator amplifier to the input of a second, similar, tworesonator amplifier, a cascaded amplifier having,

three resonators constitutes a much better way of accomplishing the same result. Bot'h stages of amplification are thus located within the same vacuum envelope, and they use the same electron beam. The middle resonator abstracts power from the beam as theoutput cavity of the first stage, and the R. F. voltage developed in the gap therein proceeds to velocity-modulate the beam as the input-gap voltage of the second stage.

This arrangement has the advantages that there is one electron beam used instead of two, there are three cavity resonators to tune instead of four, and the gain can be made more than fourtimes as great as it would be in the coupled two-resonator amplifiers because of improved bunching.

Recessed bores or passages I0, II and I2 are located at a side face I3 of body I to receive the energy coupling members I4, I5 and 16. The coupling members I4, I5 and I5 serve to couple cavity resonators 2i, 22 and 23, respectively, to external apparatus (not shown). A vertically extending passage or bore 2 serves to receive the re-entrant posts 3, 4, 5 and 6, the posts being in the form of metal sleeves which carry electronpermeable electrodes or grids I1, I8, I9 and20 at the ends thereof. Successive posts define pairs; to wit: 3 and 4, 4 and 5, and 5 and 6, extending into cavity resonators "2I, 22 and 23, respectively', to define an electron stream passage 6 along a path or line intersecting the tubular inner surface of the cavity resonators. Prefabricated diaphragmstampings 24 and 25 eachhaving three diametrically aligned annular undulations 26, 2'! and '28, are mounted upon theopposi-te broad faces -29, 30 of body I. The st ampings 24, 25 form end walls for the tubular-shaped inner surfaces of bores I, 8 and 9 to define the drum--, shaped cavity resonatorsZI, 22 and -23.' Prefabricated outer face stampings 3| and 32 are mounted upon the diaphragm face stampings24, 25 respectively. Differential screw assemblies 33 are carried by face stampings 3|, 3-2 for the purpose of flexing the resilient portions of diaphragm stampings 24, 25 to tune the drum-shaped cavities is desired frequencies. a

A cathode assembly 34 is shownattached and sealed vacuum tight to the lower end of body I.

Cathode assembly'34 comprises a multi pronged base 35, a cathode button 36 as a source of electrons for emitting an electron stream along a substantially linear path within the tubular posts 3, 4, 5 and 6, cathode button heater apparatus 31 and a focussing shield 3-8 that minimizes electron beam spreading. The accelerator grid I1 is disposed in the path of the electron stream, and is attached by brazing to the end of tubular post 3 nearer the cathode assembly 34. A metal cap 39 is mounted at the other end of body I, at the mouth of bore 2, and it is sealed vacuum tight thereat toclose the opening and to serve as a electron stream absorber.

The outer or end coupling members [4, I6 and the middle coupling member I5 couple the outer or end cavity resonators 2|, 23 and the middle cavity resonator 22, respectively, to external apparatus (not shown). The middle energy coupling member I5 is positioned in bore I I with an inner end thereof abutting the shoulder 41. Member I5 may consist of any suitable, conventional coupling assembly. The assembly described in copending application Serial No.

573,734, filed January 20, 1945, in the name of L. F. Sorg, now Patent No. 2,490,845, granted December 13, 1949, is shown. An inner conduotor-45 extends into the floating cavity resonator 22. Within the resonator 22, the inner conductor 45 is bent to form a small magnetic cou- :an external source, nor does it supply energy to an external load.

As shown in Fig. 3, the outer or end coupling members I4 and I6 are positioned in the recessed bores Ill and I2, respectively with inner ends thereof abutting the shoulders '41. Coupling members I4 and I6 may likewise includea coupling assembly of the type disclosed and claimed in the aforementioned patent to L. F. Sorg to couple cavity resonators 2I and 23 to external a-pparatus (not shown). However, as shown in 3, inner conductors 5-3 of theouter coupling members I4, I6 extend into cavity resonators 2-I, 23 and are soldered at their free ends 54 to the tubular posts 3 and 6 as probes, Asa result of the geometry of the drum-shaped cavity resonators, a probe connected'to the tubular posts gives adequate coupling. Fig. 3 shows that the longitudinal axes of coupling members I4 and I6 are not in the diametral plane of the cavity bores 1 I and 9; instead, the inner conductors 53 are offcharge considerations are treated.

7 of coupling, therefore, may be varied by changing the amount of off-setting of bores l0, l2 during the fabrication of the conducting body I.

The electron-permeable electrodes or grids l8, l9 and 20 are pre-assembled on the insert posts 3, 4, 5 and 6, and are secured thereto by brazing. After the body is machined, the posts 3, 4, 5 and 8 carrying the grids l1, l8, l9 and 20 are properly located in the bore 2 with the aid of a jig (not shown). Clamping screws 55 aid in holding posts 3, 4, 5, 6 in position until the posts are soldered or brazed at the joints they make with the conducting body Grids |8, l9 and 20 are located at adjacent ends, respectively, of posts 3, 4, 5 and 6 to support radio frequency voltages defined by the electromagnetic fields of the cavity resonators 2 22 and 23. In structure, these electrodes may be of any suitable well known or conventional design, such as of spoke-shaped or honeycomb design, or they may be pyramid grids of the type disclosed and claimed in a copending application entitled Grid Structure and Method of Fabrication, Serial No. 740,560, filed April 10, 1947, by F. W. Salisbury, now Patent No. 2,515,267, granted July 18, 1950. In the disclosed embodiment of Figs. 1-3, pyramid grids of the type disclosed in said Patent No. 2,515,267 are used.

Grids I8 and I9 are made with one layer of triangle folds of vanes 56 for the purpose of optimizing beam current transmission, and in contrast, grids 20 associated with the output cav-- ity resonator 23 include two layers of triangle folds of vanes 58 (note Fig. 3A) for the purpose of optimizing coupling. At the output cavity resonator 23, dense vane grids 20 defining relatively high coupling are used to afford relatively high gain even though beam current interception, as a consequence, is relatively high, because, at the output stage, high gain is desirable and beam current interception is no longer pertinent. This arrangement aids to increase the output efiiciency of the amplifier tube. Accelerator grid H includes a double layer of triangular-fold vanes, because a fine mesh grid is required at this point to reduce beam aberration.

The drift distance has an important bearing on the gain, output and efficiency of the amplifier discharge tube. Therefore, it is desirable to maintain electronic transadmittance (the ratio of the output-gap driving current to the input-gap voltage), which is related to drift length, at a maximum for the amplifier stage and at an optimum for the output stage, As a consequence, the drift tube length of the amplifier stage, which is determined by post 4, and the drift tube length of the output stage, which is determined by post 5, should be unequal; the former should be slightly longer-than the latter. At the amplifier stage, where maximum electronic transadmittance is desired, the drift tube length is controlled by weak signal theory where longitudinal debunching predominates; whereas, for the output stage, the drift tube length is controlled by strong signal theory where transverse debunching or space Reference may be had to Klystrons and Microwave Triodes, volume VII, the M. I. T. Radiation Laboratory Series for a comprehensive discussion of the dependence of electronic transadmittance on drift lengths.

The amount of projection of successive re-entrant posts 3 and 4, 4 and 5, 5 and E into the cavity resonators 2|, 22 and 23, respectively, may be made equal to locate the R.-F. voltage gaps at the center of the cavity bores I, 8 and 9. However, it will be understood that by locating the cavity bores 8 and 9 at proper distancesapart, and by varying the physical lengths of the reentrant posts 3, 4, 5 and 6, the re-entrant posts may be made to project unequal lengths into the cavity resonators to off-set the R.-F. voltage gaps with respect to the cavity bores.

The inner diameter of the tubular posts 3, 4, 5 and 6 is controlled by the amplifier conditions desired, and is determined by the well-known engineering techniques available to the tube designer.

The dimensions of the drum-shaped cavity may be derived from the equations of a square prism resonator. This is possible because the corner efiects of the square resonator are negligible, and therefore may be neglected. As a consequence, the longitudinal length and the diameter of the cavity resonators 2 I, 22 and 23 are approximately equal, and the outside diameter of the re-entrant posts is appreciably less than the diameter and longitudinal length of the cavities.

The undulations 26, 21 and 23, aforedescribed, are made by a punch press operation for the purpose of making the portion of the thin stampings 24, 25 juxtaposed to the openings 1, 8 and 9 flexible so that these portions may serve as diaphragms 59, 60 and (SI for tuning the drumshaped cavity resonators 2|, 22 and 23. The outer face stampings 3|, 32 have three diametrally aligned openings 63, and they are mounted upon the diaphragm stampings 24, 25, respectively, and are removably secured to the opposite sides of the conducting body by bolts 51 threadedly engaging holes 58.

The face stampings 3|, 32 carry mechanical devices (differential screw assembly 33) at each of the three diametrally aligned openings 63 for activating the diaphragms 59, 60 and 6| of each of the cavity resonators 2|, 22 and 23. For fine trim tuning of the cavities, it is desirable to apply Very slight axial or translational motion to the diaphragms 59, 80, 6|. The differential screw mechanism makes this possible without using screws having exceptionally fine pitch and weak threads. Thus it is possible to tune the cavity resonators 2|, 22 and 23 with bolts or machine screws having coarse threads that will stand up under hard and frequent use.

The assembly of a differential screw tuner includes an outer tubular jacket or sleeve 62 rigidly mounted by brazing at an opening 63. The inner end 64 of jacket 62 abuts the outer surface of a diaphragm stamping. Jacket 62 has a threaded inner surface 65 of a first pitch, for example, 20 threads per inch. A nut 66 having a threaded outer surface 61 engages the inner surface 65 of jacket 62. Nut 66 also has a threaded inner surface 68 of a second pitch, for example, 25 threads per inch. A sleeve 69 having a threaded outer surface 10 engages the threaded inner surface 68 of nut 86. Each of the diaphragm stampings 24, 25 carries a rod H in coaxial relationship with respect to the annular undulations 26, 21 and 28. The rods H are rigidly secured by brazing to the center of the diaphragms 59, 60 and 6| at openings .2. Sleeve 69 has an inner surface 16 defining a bore that serves to receive rod 1|; the sleeve 69 and rod H are firmly secured together by soldering. This arrangement prevents the sleeve 69 from rotating. The slots 13 on jacket 62 and the longitudinally extending slots 14 on nut 66 mechanically load the threads of the differential screw assembly to take up back-lash. The radially extending slots 14 on the face of nut '9 66 serve .to receive a complementary embossed screw driver (not shown) so that rotational motion may be imparted to nut 66.

By turning nut 66, thedifierential screw mechanism converts the rotational motion at nut 66 to axial or translational motionat sleeve 69, rod II accordingly, the connected diaphragm is flexed. For example, one complete clockwise turn of nut 66 carries the nut .050 inch to the left. ,In effect, nut 66 also travels on the threaded sleeve 69 a distance of .040 inch. The diiference, which is .010 inch, is made up by translational motion of sleeve 69 and rod 11 to the right; accordingly, the center of the connected diaphragm is pulled out a distance .010 inch.

The method developed for tuning the drums-haped cavity resonators 2|, 22 and 23 consists of varying the volume of the cavities. The tuning effect depends upon the location of the'diaphrag-m in the electromagnetic field supported by the cavity. If the diaphragm is flexed to decrease the cavity volume in a region of high magnetic field, the frequency of oscillation increases. .In terms of lumped-constant equivalent circuits, a decrease of volume of the cavity in a region of high magnetic field decreases the equivalent inductance which in turn increases theresonant frequency of the equivalent circuit. When the diaphragm is flexed to'decrease the cavity volume in a region of high electri-cfield, the frequency of oscillation is increased. In terms of the lumpedconstant equivalent, this corresponds to a decrease in capacitance.

In the disclosed embodiment, the diaphragms 59, 6.0 and 6| move in a region of high magnetic field, and this type of tuning .is sometimes :referred to .as inductance tuning. It will be understood that a comparatively larger motion is required of the-diaphragms 59,160 and 6-] for a given tuning range for inductance tuning as compared with that required in capacity tuning. This feacure is advantageous because it,.provides finer tuning control. A further-advantage is that the induc-tance tuning is substantially linear, whereas the capacity tuning may not be linear, but may follow some exponential relationship. In order to get the required tuning range, it isnecessary that diaphragms 59, 60 and :6 I be located properly to give maximum effect. For instance, if the diaphragms arelocated too close to there-entrant posts, the efiect is .to produce capacity tuning as well as inductive tuning. These two effects tend to cancel each other, and thereby reduce the effective tuning range. Consequently, the .diaphragms are removed from'there-entrant posts 29 so that 1 they move only in a region .ofhigh magnetic field.

Although the cavity resonators 2|, 22 .and '23 of the illustrated embodiment are shown to incorporate two individual tuning assemblies at each end wall, it will ,be understood that "this arrangement is merely "a matter of choice. 'A modification of the disclosed embodiment may include one tuning assembly for ea'ch cavity. In this instance, face stamping 3| may carry the tuning assemblies 33, as illustrated in Fig. land the coupling members H, 15 and II Gamay then be mounted on face 30 of body I. Accordingly, the, diaphragm face stamping :25 is omitted, and face stamping .312 is secure and sealed by brazing to face 3 0 ofbo'dy I. Facestamning-M would have openings corresponding to the openings 10, H and I2 instead of locating these --openings at the side wall 1-3 of body Land .the coupling members I4, I5 and .IB would then be mounted .on the face stamping 32 to couple thecavity resonators 2 I, '22 and 23 to external "apparatus,

Figs. 6 and 7 illustrate a three-resonator dis charge tube in which only one of theend walls of each cavity is used for tuning the cavity resonators. This embodiment in other aspects illustrates further modifications of the embodiment of Figs. 1-5. In this instance, the outer shape of the drilled or bored block of conducting material I .is semi-cylindrical and acathodeassembly 34 isattached thereto. Three-diametrally aligned bores I, 8 and 9 and end walls .59, .60, .GI and define the three drum-shaped cavity resonators2l, 22 and 23. The aligned tubularconducting :posts 3, 4, 5' and 6 define the electron stream path extending along a line intersecting the tubular inner surfaces of bores I, 8 and 9. Accelerator grid I1 is mounted at the end of the post3 nearer the cathode assembly 34. The adjacent ends of re-entrant posts 3,-.4, 5 and. .6. projecting into the successive cavity resonators 2|, .22, 23 carry grids l8, I9 and respectively. The cavities are coupled to external apparatus (not shown) by .cou-plingmembers I5 which communicate with the cavity'reso- .nators, through the end walls 15 of the resonator assembly. Absorber cap 39' seals the top of the resonator assembly and serves to absorb the electron stream. The circumferential edges .of diasembly, the block .of conducting material! rest- .ing on its fiat .face 84 is placed in a jig .(not shown), and it is drilled and bored to the depth of shoulder 11 to define the outer openings 1a,.8a, .9a.

Thesmallerinner boresl, 8 and 9 are subsequently drilled .to define the inner tubular surfaces of the cavity resonators 2|, .22 and 23' and shoulders .'I1.- .A further drilling process dofines the openings in the end wall 75 tofreceive the coupling connectors I5; A vertical bore is :drilled for the purpose of receivingthe re-entrant posts 3, 4, 5 and 6'. posts .3, 4, .5 and 6 carryinggrids I 1 t8, I9 and .20 are inserted into the opening therefor, and they are located in the drilled block with the aid'of --a jig '(not shown); The re-entrant posts-are firmly secured by brazing at the joints they make with the drilled block. Absorber cap 38, coupling ;members .15 and diaphragms 58, 60' and v6| areyproperly mounted to .seal the cavity resonators. Subsequently, the tuning .as-

sembly is attached to the cathode assembly.

ito r-make :the cavity resonator structure from .pre-

It is within the scope of the present invention fabricated tubular conducting bodies and face s-tampings'as illustrated in Figs. 8 and v9. Three I largegtubular conducting bodies .90, BI and 82 have inner surfaces ".93, stand :defining the inner surfaces of the vacuumtight, drum-shaped cavity resonators 3659.1 -an'd=98. Smaller tubular stream passage. Post 102 is closed at far-end re-entrant posts, and they define the electron I30 to'serve as the electron beam absorber. Fo-r Tocussing purposes and for the purpose of preventing debunc'hing of the electron stream, the inner diameter of post 89 and a portion of post The re-en-trant I is made slightly larger than the inner diameter of the remaining portion of post I00 and posts IOI and I02.

Each of the larger tubular conducting bodies supports two smaller tubular posts; the latter extend toward each other into the cavity chambers from opposite regions of the tubular inner surfaces of the cavities to define R.-F. voltage gaps. These tubular assemblies are firmly secured by brazing at the joints the re-entrant posts made with the cylindrical surfaces of the larger tubular bodies. An accelerator grid I03 is firmly secured by brazing at the end of reentrant post 99 nearer the cathode structure 34. The remaining grids I04, I and I06 are secured by brazing at the adjacent ends of the re-entrant posts extending into cavity resonators 96, 91 and 98, respectively.

The larger tubular conducting bodies 90, BI and 92 are enclosed by face stampings I01, I08, I09, IIO, III and H2 with the inner surfaces 93, 94, 95 of the tubular bodies in diametral alignment and with the re-entrant posts 99-!02 in linear alignment. Accordingly. a hollow interior H3 is defined between the inner surfaces of the face stampings and the outer surfaces of the assembled tubular bodies. The entire cavity structure is firmly secured together by brazing the abutting joints of the face stampings and the tubular assemblies.

Diaphragms H4, H5 and H6 having undulations I23 are mounted at one end of each of the conducting tubular bodies 90, 9| and 92 to define one of the end walls of the cavity resonators. The diaphragms are firmly secured at their circumferential edges to the bevelled edges N1 of the tubular bodies 90, SI and 92 by brazing. Differential screw assemblies 33 are mounted upon an outer face stamping I I8 at three aligned openings therein juxtaposed to the open ends of the inner surfaces 93, 94 and 95, and the differential screw assemblies serve to activate the diaphragms II 4, I I 5 and I I6 for the purpose of tuning cavities to the desired frequencies of operation. The differential screw assemblies 33 may be identical with the differential assemblies disclosed in the embodiment of Figs. 1 to 5, and each includes the slotted outer jacket 62, the slotted nut 66, sleeve 60 and rod II which has one end thereof firmly connected to the center of a diaphragm.

Outer face stamping H8 is removably secured to face stamping I01 by means of tap bolts H9. The cathode assembly 34 is attached to the face stamping I09. Cavity resonators 96, 91 and 98 are coupled to external apparatus (not shown) with the aid of coupling members I20, I2I and I22 mounted on face stamping I08. Coupling members I20, I2I and I22 are terminated with coupling loops I24, I25, I26, respectively. Loop I25 of member I2I may be made relatively small, and it projects only slightly into the middle resonator 91 because it is merely used to monitor the floating cavity resonator 91. The center conductor I3I and the terminating loop I26 of coupling member I22 are made of a heavy conductor to permit heavy current duty at the output cavity resonator.

A cooling fluid may be circulated in the hollow interior I I3 for the purpose of cooling the cavity resonators during the operation of the tube. Therefore, opening I21 located in face stamping H0 and a conduit I29 mounted at opening I21 and projecting into the interior II3 serve to direct the cooling fluid into the hollow interior H3. The cooling fluid leaves the hollow interior 12 H3 through opening I28. The pinched off tube I32 communicates with the interior of the cavity resonators 86, 91 and 98 and. it is used for evacuating the electron discharge tube.

It is within the scope of the present invention to mount one differential screw assembly on an outer face stamping, for example, face stamping 3I of the Figs. 1 to 5 (or face stamping I08 of Figs. 8 and 9) and have the sleeve 09 of the differential screw assembly .33 linked to the three rods II that are connected to the three diaphragms 59, B0 and GI. This arrangement offers a very simple method of gang tuning the cavity resonators.

In operation, the beam of electrons emitted from the cathode is first accelerated to a high velocity by a D. C. potential (not shown) applied to the accelerator grid. The beam then passes through the first interaction gap in the input resonator of the discharge tube where each of the electrons receives additional acceleration (positive or negative) depending upon the phase and magnitude of the R.-F. voltage at the gap during the passage of the electrons. Accordingly, thevelocities of the beam electrons are varied. The electrons then traverse the first drift tube in which the variations of velocity of the electrons give rise to density modulation or bunching. Subsequent interaction takes place at the second R.-F. voltage gap at the middle resonator, and the beam of electrons is further modulated; then the bunched electrons traverse the next drift space defined by the second drift tube. Interaction of the bunched beam of electrons at the third gap with the electromagnetic field in the third cavity energizes the third or output cavity. From the third gap, the beam traverses the last insert post to be absorbed by the absorber element. The R.-F. voltage at the input gap is defined by the electromagnetic field in the first cavity, and this cavity is energized from an outside source coupled to the first cavity. Energy may be transferred from the third cavity to a load by means of the coupling connector communicating with the cavity.

In a particular example, the disclosed discharge tubes may be used as straight amplifiers; that is, some small signal of frequency F1 is coupled to the input cavity, and by the operation of the discharge tube, an output signal of frequency F1 of greater amplitude is derived from the output cavity. The same structures may also be used as a synchrodyne amplifier. In this instance, an input signal of the frequency F1, as before, is coupled tothe input cavity by the coupling connector communicating therc'lvith; a second and lower frequency signal of frequency F2 is connected in series with the cathode of the sychrodyne amplifier to produce phase modulation sidebands. The middle and output cavities are then tuned to one of the adjacent sidebands produced by the modulation process, for example, the first upper band. The output power available at the output cavity is at frequency F3 which differs from the input frequency F1 by the frequency of modulation F2. It will be understood, however, that the disclosed structures are in no way limited to the two aforesaid uses, and furthermore that the present invention is in no way limited to a three-cavity resonator assembly. It is within the scope of the present invention to limit the cavity assembly to two resonators for the purpose of making a two-resonator discharge tube, and it would be equally simple to construct a. single resonator unit pursuant to the present invention.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that .all matter contained in the above description or shown in the accompanying drawings shall be interpreted .as illustrative andnot in .a limiting sense.

What is claimed'is: v

1. Microwave tube structure comprising a conductive block having a plurality of cylindrical bores therethrough, conductive means extending across and closing the ends of said bores, the bores with closed ends providing a plurality of enclosed cylindrical resonant cavities, the bores having their respective axes of; revolution perpendicular to and intersecting .a common axis','the block having a transverse bore extending along said common axis and intersecting each of said resonant cavities, and a series of aligned cylindrical sleeves positioned in said transverse bore, the sleeves having their ends terminating in the resonant cavities, adjacent ends of the series sleeves being spaced slightly from each other to define a single gap within each of the'resonant cavities.

2. Microwave frequency cavity resonator apparatus comprising conducting means having a plurality of cylindrical bores, the axis of revolution of each of the cylindrical bores being perpendicular to a common axis, said axes of revo-- lution intersecting said common axis at spaced points, conductive mcansproviding end walls for each of said bores, the'end walls and bores defining discrete cavity resonator chambers, at least one of said end walls in each of the resonator chambers being flexible for tuning the respective resonators, and a series of conductive sleeves extending along said common axis, each of the chambers having a single capacitive gap therein defined by the adjacent ends of two of the sleeves in the series.

3. Microwave frequency tube structure comprising hollow conductive means having a plurality of diametrally aligned tubular-shaped inner walls and end walls defining a plurality of discrete cavity resonators, said tubular-shaped inner walls extending in a parallel relationship to a straight lengthwise axis, and each of said end walls being located at opposite correlated ends of said tubular inner walls, means emitting an electron stream along a linear path intersecting said tubular-shaped inner walls, a series of aligned hollow posts extending along and surrounding said electron stream, successive ones of said posts defining pairs extending into suecessive resonators from opposite tubular-shaped I inner wall portions thereof, theadjacent ends of said pair of posts being terminated just short of each other Within the correlated cavity reso-, nator to define in each of said resonators a single energy interchanging gap, electron-permeable electrodes at said adjacent ends of said pairs of posts, one of said end walls being flexible for tun- 7 ing the correlated resonator to frequencies of operation, and means for coupling the correlated resonators to external apparatus. I

4. Structure as defined in claim 3 further including means for flexing the flexible end walls including a relatively motionless sleeve having a threaded inner surfaceof a first pitch, a nut having a threaded outer surface for engaging said sleeve and also having a threaded inner surface'of 514 a second pitch, a. further sleeve having a threaded outer surface for engaging the said threaded inner surface of said nut, and means for preventing rotational motion of said second sleeve including a rod connected to the correlated flexible end wall and to said second sleeve, whereby rotational motion imparted to said nut is converted'to axial motion at said second sleeve to flex said 'con-.

nected end wall. 1

5. Microwave frequency cavity resonator structure comprising an assembly of two types of hollow conducting bodies, face stampings enclosing, said assemblage, the outer surface of said assemblage and the inner surfaces of said face stampings defining a hollow interior therebetween, the first of said types of said bodies each having a tubular inner surface defining the tubular inner surface of a cavity resonator, the second type of said hollow conductive bodies-extending into said cavity resonator from the opposite regions of the tubular inner surface of said resonator to define a single capacity loading section in said resonator,

two of said face stampings being positioned at the opposite open ends of said tubular inner surface, at least one of the last-mentioned face stampings having an opening j uxtapositioned to the adjacent of said open ends, and a diaphragm located at said adjacent open end of said resonator.

6. Microwave frequency cavity resonator struc ture comprising an assemblage of two types of tubular conducting bodies, face stampings enpair of said face stampings being positioned at the I opposite open ends of said cylindrical inner surfaces, and at least one of the last-mentioned face stampings having an opening juxtapositioned to the adjacent of the open ends of said cylindrical inner surfaces, and diaphragms mounted at said adjacent open ends of said cavity resonators.

7. Microwave frequency cavity resonator structure comprising a block of conducting material having a tubular inner wall extending therethrough in a parallel relationship toa straight lengthwise axis, conductive end walls positioned at the opposite'open ends of said tubular inner wall, one of said end walls having a flexible portion juxtaposed to the adjacent of said open ends, and a pair of conducting arms directed into the chamber of said cavity resonator from oppo site regions ,of said tubular inner wall thereof, the adjacent ends of said pair of arms being spaced to'define a capacitive gap within the'chamber.

8. Microwave frequency cavity resonator structure comprising a block of conducting material having a plurality of diametrally aligned cylindrical inner walls extending therethrough in a parallel relationship to a straight lengthwise axis, conductive end walls positioned at the opposite open ends of said cylindrical inner walls, one of said end walls having flexible portions juxtaposed to the adjacent of said open ends, and a series of aligned posts defining a single capacity loading section for'each of said resonators, each of said resonators having two posts of said series extending therein from opposite regions of the cylindrical inner surface thereof, and the adjacent ends of said two posts being terminated just short of each other to define said single capacity loading section.

9. Microwave frequency tube structure comprising a block of conducting material having a plurality of diametrally aligned cylindrical inner walls extending therethrough in a parallel relationship to a straight lengthwise axis and defining the cylindrical inner walls of discrete cavity resonators, conductive end walls positioned at the opposite open ends of said cylindrical inner walls, one of said end walls having a flexible portion juxtaposed to the adjacent of said open ends for tuning the correlated resonator to desired frequencies of operation, a series of aligned hollow posts defining an electron stream path, each of said resonators having an energy interchanging gap therein defined by the adjacent ends of two posts of said series extending therein from opposite regions of the cylindrical inner wall thereof, said adjacent ends of said two posts being terminated just short of each other, and means emitting a linear beam of electrons along said path.

10. Microwave frequency tube structure comprising a block of conducting material having a plurality of diametrally aligned cylindrical inner walls defining the cylindrical inner walls of cavity resonators, conductive end walls positioned at the opposite open ends of said cylindrical inner walls, said end walls having a flexible portion juxtaposed to the adjacent of said open ends for tuning the correlated resonator to desired frequencies of operation, a series of aligned posts defining an electron stream path, each of said resonators having two posts of said series extending therein from opposite regions of the cylindrical inner wall thereof, means emitting a linear beam of electrons along said path, outer face stampings positioned at said end walls, said outer face stampings having openings aligned with said end wall flexible portions, and means mounted at said openings in said outer face stamping for activating said flexible portions.

11. Microwave frequency discharge tube apparatus comprising an assemblage of a plurality of tubular conducting bodies, face stampings enclosing said assemblage, the outer surfaces of said assemblage and the inner surfaces of said face stampings defining a hollow interior therebetween, at least one of said tubular conducting bodies having a cylindrical inner surface defining the cylindrical inner surface of a cavity resonator, two other of said bodies being directed into the interior of said cavity resonator from opposite regions of its cylindrical surface to define an elec tron stream path, two of said face stampings being positioned at the opposite open ends of said cylindrical inner surface to form end walls therefor, at least one of said end walls having an opening aligned with the adjacent of said open ends of said cylindrical inner surface, a diaphragm mounted at said adjacent open end of said cylindrical inner surface for tuning said cavity resonator to a desired frequency of operation, and means emitting a linear beam of electrons along said path.

12. Microwave frequency tube structure comprising an assemblage of a plurality of different types of hollow tubular conducting bodies, face stampings enclosing said assemblage, the outer surfaces of said assemblage and the inner surfaces of said face stampings defining a hollow interior therebetween, the first type of said tubular bodies each having a cylindrical inner wall extending in a parallel relationship to a correlated straight lengthwise axis defining the cylindrical inner walls of cavity resonator chambers, said first bodies being positioned with their cylindrical inner walls in diametral alignment, the second type of said tubular bodies being aligned to define a linear electron stream path, each of said resonator chambers having an energy interchanging gap therein defined by the adjacent ends of two of said second type of tubular bodies directed therein from opposite regions of the cylindrical inner wall thereof, said adjacent ends of said two bodies being terminated just short of each other, two of said face stampings being posi- .tioned at the opposite open ends of said cylindrical inner walls to define end walls therefor, and at least one of said end walls having an opening aligned with the adjacent of said open ends of said cylindrical inner walls, diaphragms mounted at said adjacent open ends, and means emitting a beam of electrons along said path.

13. Apparatus as defined in claim 12, further including means mounted at the diaphragm openings for activating the diaphragms, means mounted on the other end Wall remote from said diaphragms for coupling the correlated cavity resonators to external apparatus, and means for cooling said cavity resonators during the operation of said microwave frequency tube by circulating a cooling fluid through said hollow interior.

l4. Microwave frequency tube structure incorporating a cavity resonator comprising an assemblage of two types of hollow conducting bodies, the first of said types of bodies having a cylindrical inner wall extending parallel to a straight lengthwise axis, face stampings mounted at the open ends of said cylindrical inner wall and forming therewith a cavity resonator, means characterized by a pair of conductive bodies of the second type defining a single energy interchanging gap within said cavity resonator and also defining an electron stream path, each body of said pair extending into said cavity resonator from opposite sides of said cylindrical inner wall thereof with the adjacent ends of said second type of bodies terminating just short of each other, and means for producing a stream of electrons for passage within said pair of bodies and through said gap.

15. Microwave tube structure comprising a block of conducting material having a pair of parallel outer surfaces, the block having a first cylindrical bore extending between said surfaces, conductive plate means secured to each of said surfaces and closing off the ends of the bore, the block having a second bore substantially transverse to and intersecting said first bore, a pair of sleeves secured in said second bore, the sleeves extending into the first bore with their adjacent ends spaced apart for providing a capacitive gap within the first bore, and means adjacent one end of the second bore for directing a stream of electrons longitudinally through said sleeves and across said gap.

16. Microwave frequency tube structure incorporating a plurality of discrete cavity resonators comprising a prefabricated block of conducting material having a plurality of diametrally aligned cylindrical-shaped inner walls extending therethrough, each of said cylindrical inner walls extending in a parallel relationship to a correlated straight lengthwise axis, a plurality of conduct- 1? 7 ing end walls positioned at the opposite open ends References Cited in the file of this patent of said cylindrical inner walls, means emitting a UNITED STATES PATENTS stream of electrons through the cavity resonators, and a series of aligned hollow posts defining an Number Name Date electron stream path, each of the cavities having 5 2393949 Lltton l 13, 1942 two posts of said series extending therein from 2,303,523 Llewellyn -r 1943 opposite regions of said cylindrical inner wall 2 6 Fremlln June 1943 thereof, the adjacent ends of said two posts be- 2,333,343 Ryan v1945 ing terminated just short of each other to define o ggg itfigr 'liI 2 3 in r s a a single energy interchanging gap te posed aid 10 2475562 v a et a1. u; July lz, 1949 stream.

SIGURD V 2,486,398 Feenberg NOV. 1, 1949 

